ScoobySport's Low Catalyst Efficiency Electronic Fix

[Jon [in CT]]

Attached below is a diagram I made which I believe represents the electronic circuit ScoobySport has developed to eliminate the CEL when you have no cats. Three identical 1.5M Ohm resistors are used in series because I couldn't find anyone that sells a 4.5M Ohm resistor (and besides, you usually have to buy at least 5 ).

I myself haven't even seen the ScoobySport fix yet and I haven't tried the circuit, below, myself. And I have a request for those with electronics skills who will be buying these little boxes from ScoobySport in the near future. Please make some capacitance and resistance measurements on the various leads and let me know whether you can confirm that I got the circuit right.

P.S.

B17 is the ECU's input from the rear O2 sensor
D3 is a 12V ECU output

[zaxrex]

I think I was awake when some physics teacher said that temperature changes will influence resistivity in a circuit. Where is this "magic box" mounted? If near the exhaust, would the temp extremes have an effect on this trick?

[mitch808]

yes heat will increase resistance. I dont see why you cant mount this with the ECU under the carpet, sounds like a great location there is lots of room there

[lenyx]

It has to be mounted near the ecu.. the wires aren't all that long, and there's no reason to put it anywhere else.

[zaxrex]

Cool, thanks.

[Jon [in CT]]

Sorry. I should have explained a little more.

The ScoobySport "black box" attaches to the wiring at the ECU, under the mat in the passenger (RH) side foot well. It has four wires, colored orange, yellow, black and blue. Thus, it lives inside the passenger compartment and its temperature should be relatively stable by the time the ECU decides conditions are ripe for testing the cat system efficiency.

The method of attachment is:
1) Cut the wire with white insulation leading from ECU pin B17 (see WRX ECU wiring diagram at www.Ravensblade.com, www.projectwrx.com and elsewhere). That white wire carries the sensor signal from the rear O2 sensor to the ECU.
2) Attach the orange wire from the "black box" to the ECU-side white wire.
3) Attach the blue wire from the "black box" to the sensor-side of the white wire.
4) Attach the yellow wire from the "black box" to the 12V wire from the ECU with yellow insulation and blue strip (only remove insulation; don't cut the wire).
5) Attach the black wire from the "black box" to a good chassis ground.

All the info I have arrived unsolicited via email:

... a reading of 4.55 meg Ohms was obtained between the blue and orange wires from the fix-it box, so they've run a 4.5M ohm resistor in series with the rear O2 sensor. A reading of 3.36 micro Farads was obtained between the yellow wire and the black ground wire. It's an electrolytic capacitor, as an open reading was obtained when the meter's leads were reversed.

Those appear to be pretty precise measurements. The writer also reported that the design and instructions were claimed to be copyrighted, which probably explains why the writer was reluctant to be identified. Probably a Brit - these are probably already on the street in the UK and you know how "concientious" the Brits can be about copyrighted web pix.

[lenyx]

That's not entirely true.

There are about 4 more wires coming out of the box that are unused.. and are about half as short. I'm not sure what their purpose is.

[Jon [in CT]]

lenyx,
I believe you're correct. My correspondent told me it was a :

Plastic box measuring 3cm deep x 2.5cm tall x 5cm wide, with one stuffing tube and eight wires. The box was made in a proprietary manner, which is to say that it was filled solid with black goop/plastic junk, defeating the efforts of all prying eyes.

I had assumed that, since only 4 wires were connected to anything, that my correspondent had made a small mistake.

So, lenyx. It seems you have one. What else can you report?

[lenyx]

Umm.. it's grey in color.. and uh.. yea... that's about it for what hasn't been said.

I spent last weekend building a wiring harness for it and my unichip and avc-r so that I could keep all my ecu wires organized and do away with a mess of butt connectors and splices.

I won't actually have anything to report on functionality until I finish putting the appropriate connectors on the ecu wires and plugging everything in. That will hopefully happen this weekend.

Although I'm not even sure if I'm still getting the low catalyst cel anymore.. ever since I installed my up-pipe the cel has been oddly quiet.

Is it possible to make the splices in the corresponding wires on the unichip? I would prefer to make the connections there, if possible, and keep from altering the factory ecu wires. But, I imagine since it's a piggyback unit, I will not be able to. Thanks for any help.

[lenyx]

Originally posted by Tex-WReX2
Is it possible to make the splices in the corresponding wires on the unichip? I would prefer to make the connections there, if possible, and keep from altering the factory ecu wires. But, I imagine since it's a piggyback unit, I will not be able to. Thanks for any help.

If you have the turboxs unichip and harness I suppose you can. A unichip w/out harness doesn't call for splicing the same wires as the cel fix.

[Thumper]

Jon,
Are you sure that black wire goes to ground? Seems that the return voltage would just go there and not to the ECU, or am I missing something here?

What would the resulting voltage be for a return signal of .7V or .3V? Just curious to see what's happening.

[lenyx]

The black wire is indeed a ground. Has a ring terminal and everything.

[Austin]

Hmmm....

[Jon [in CT]]

Originally posted by Thumper
Jon,
Are you sure that black wire goes to ground? Seems that the return voltage would just go there and not to the ECU, or am I missing something here?

What would the resulting voltage be for a return signal of .7V or .3V? Just curious to see what's happening.

Thumper,
I'm not sure about anything here, since I don't have one. For instance, I'm not sure that the capacitor is in the correct "spot" in my diagram, above. It would, indeed, be interesting to build one of these, ground the Black wire, supply 12V to the Yellow wire, supply .3V or .7V to the Blue wire and then measure the resulting voltage at the Orange wire. But I don't have the equipment to perform that kind of test.

[worry]

This post is most amusing. I look forward to hearing how well Jon's reverse-engineered box works... or not.

worry
bbs.22b.com

[Rocky WRX]

It's obvious that Jon's schematic, as shown in the 1st post, is wrong. Take a look at the Black ground lead. It connects directly to the Orange/White/ECU-B17 lead. With the circuit as shown, the ECU's rear sensor input will always be grounded.

It would be useful to have resistance measurements between the black lead and the orange lead, and between the black lead and the blue lead. Then Jon could refine his schematic accordingly.

[pat]

Hi All!

Simply using a few passive devices to get round the CEL problem isn't necessarily the best approach (perhaps even dangeroous), because whatever the circuit achieves it can only ever be a linear function of the original input voltage from the O2 sensor, which is obviously "wrong" otherwise it wouldn't be causing the CEL to come on. I would advise against fitting a simple passive device, because any passive configuration capable of alleviating the CEL problem will also distort the ECU's lambda readings, which it uses for fuel trim.

Cheers,

Pat.

[Jon [in CT]]

Originally posted by pat
I would advise against fitting a simple passive device, because any passive configuration capable of alleviating the CEL problem will also distort the ECU's lambda readings, which it uses for fuel trim.

Here's what I believe is the function of the rear O2 sensor: to confirm catalyst efficiency and, possibly, to confirm that the front A/F sensor isn't broken. I believe the ECU relies exclusively on the front A/F sensor for fuel trim feedback. For instance, if the front A/F sensor were to fail, I believe that the ECU's limp-home fallback would be to go to open-loop full-time, instead of trying to maintain a semblance of closed-loop fuel control by substituting the rear O2 sensor for the failed front A/F sensor.

And I agree with Rocky WRX. Jon needs resistance and capacitance measurements between all possible "black box" lead combinations.

[pat]

Jon,

I would agree with your assumption that the ECU would not try to use the rear O2 sensor for closed loop lambda control should it determine that the front O2 sensor has failed, because it sits (or should sit ) behind three catalytic converters, and thus will not be seeing the same appearance AFR as the front sensor anyway.

However it may use the rear O2 sensor to purge a NOx trap (should such a device be stipulated by the CARB), or for periodic regereation of the cat cores, since the rear O2 sensor gives a true post-cat appearance AFR reading, something that the front unit is incapable of. If it is used in either of these capacities then it stands to reason that the ECU does use readings to affect fuel trim for the purposes of cat / NOx trap "health".

Additionally, the distortion of the readings created by a passive device based solution could in itself create new a new CEL condition reporting that the rear O2 sensor has failed....

Cheers,

Pat.

[Jon [in CT]]

Originally posted by pat
However it may use the rear O2 sensor to purge a NOx trap (should such a device be stipulated by the CARB), or for periodic regereation of the cat cores, since the rear O2 sensor gives a true post-cat appearance AFR reading, something that the front unit is incapable of. If it is used in either of these capacities then it stands to reason that the ECU does use readings to affect fuel trim for the purposes of cat / NOx trap "health".

Additionally, the distortion of the readings created by a passive device based solution could in itself create new a new CEL condition reporting that the rear O2 sensor has failed....

The whole idea behind the electronic fix is to get around the case where the cats/NOx traps, etc. have been removed. So I don't see a problem there. And, of course, the electronic "fix" wouldn't be a "fix" if it generated a Check Engine light. So I don't see a problem there, either.

[Jon [in CT]]

A boatload of measurements have landed in my inbox. So, I'll
leave these measurements with you, 'til the morning, when I'll
have the time and attention that they deserve. A quote from their author:

The way the table is laid out, the
negative/common lead was connected to the wire on the left
hand side, and the positive lead was connected to the wire in the
top row.

For resistance, all readings are in MegOhms, except for the
Black/Orange and Orange/Black readings, which are in Ohms.


For resistance, all readings are in MicroFarads, except all the gray
wire readings, which are in NanoFarads. OL (Overload) is the
reading obtained when the leads are shorted together, and
approx 0.34 - 0.38 NanaFarads (nF) reading is obtained when
the leads are not connected to anything (separated by air).

I haven't really looked at the readings yet in an analytical
manner, but I am 100% certain that there are no typos on the chart I've attached.

  		Black (Pos+)	Blue (Pos+)	Orange (Pos+)	Yellow (Pos+)	Green (Pos+)	Gray (Pos+)	Purple (Pos+)	Pink (Pos+)
Black (Neg-)	 XXXXX		4.94M OL	140.8M OL	7.44M 3.34uF	4.95M OL	OPEN 0.48nF	5.52M OL	5.04M OL
Blue (Neg-)	3.145M OL	 XXXXX		3.145M OL	17.80M OL	12.31M 4.55uF	OPEN 0.48nF	13.72M 4.00uF	12.44M 4.49uF
Orange (Neg-)	140.8 OL	4.92M OL	 XXXXX		7.40M 3.32uF	4.95M OL	OPEN 0.48nF	5.52M OL	5.01M OL
Yellow (Neg-)	3.815M OL	14.08M 3.99uF	3.80M OL	 XXXXX		14.12M 4.23uF	OPEN 0.48nF	15.76M 3.63uF	14.28M 4.19uF
Green (Neg-)	3.097M OL	12.08M 4.35uF	3.097M OL	17.48 1.03uF	 XXXXX		OPEN 0.48nF	13.50M 3.98uF	12.25M 4.49uF
Gray (Neg-)	1.891M OL	8.68M 3.21uF	1.890M OL	12.36 0.88uF	8.71M 3.33uF	 XXXXX		9.64M 2.88uF	8.80M 3.29uF
Purple (Neg-)	3.043M OL	11.85M 4.41uF	3.044M OL	17.18 1.04uF	11.92M 4.60uF	OPEN 0.48nF	 XXXXX		12.04M 4.55uF
Pink (Neg-)	3.084M OL	11.96M 4.35uF	3.084M OL	17.33 1.03uF	12.04M 4.53uF	OPEN 0.48nF	13.40M 3.98uF	 XXXXX

Top Row:  Positive Lead
Left Column:  Negative/Common Lead

Top Reading:  Resistance in Ohms (M=Megohm)
Bottom Reading:  Capacitance in Farads (uF=MicroFarad, nF=NanoFarad)

Open Air Capacitance reading:  0.34-0.38nF
Shorted Capacitance reading:  OL

[Ken C]

Interesting post this ...

Just a note to say that the black box is a bit more sophisticated than the initial parts of the post are noting. ScoobySport invested a good bit of time and money into development of a proper fix.

The advantage for us is not in making profit on the fix itself, but on positively and completely solving the CEL problem, which gives our exhaust a bit of an edge.

Regards,
Ken Cole
ScoobySport N.A.

[pat]

Jon,

I see your point about a fix not being a fix if it generated another CEL condition I was merely suggesting that a simple passive device based "fix" may do this, and would, by your reasoning, therefore not be a fix. Of course, if it fixes the CEL problem without creating a new CEL condition, and doesn't mess up the ECU's mixture control, then it is indeed a fix.

Your point about the fix getting round the problem where the cat / NOx trap have been removed is indeed correct, my point was that if one distorts the readings the ECU sees to fix the CEL problem, it could alter the fuelling in a way that it would never have done, were the cats still in place and it was getting true readings of appearance AFR post-cat / NOx trap.

Cheers,

Pat.

[Kartoffel]

1. Is the Scoobysport CEL-fix box for sale to everybody including people who don't have Scoobysport exhausts?

2. What does it cost?

This looks more complicated than just a simple MIL-eliminator. But.. maybe they've just thrown in extra wires to confuse people trying to reverse engineer it. If the answers to the two questions above are not satisfactory, I'd consider reverse engineering the scoobysport box. Based on Jon's measurements I'm sure we can put together a functional replica. Besides, it'd be a fun project